Question

Describe two similarities and two differences between sea urchin gastrulation, frog gastrulation, and bird gastrulation.

Answer 1

In the sea urchin,

1.       the blastoderm invaginates to shape endoderm, whose destiny incorporates the future digestive system;

2.       some cells ingress to shape mesenchyme, the future interior organs.

In the frog,

1.       vegetal cells at the blastopore involute underneath the ectoderm.

2.       Some ectoderm cells ingress to shape the mesoderm.

In the chick,

1.       the blastula is smoothed into a pocket.

2.       Outer cells (called epiblast) involute through the streak, shaping the endoderm.

3.       Some epiblast cells ingress to shape mesoderm.